The proposed studies will be concerned with three aspects of the biology of the endogenous brain peptide, thyrotropin releasing hormone (TRH). The mechanism of biosynthesis, the mechanism and control of release, and the physiological roles in poikilotherms will be studied. Little is known about TRH biosynthesis. The present evidence suggests that TRH may be the breakdown product of a large ribosomally synthesized precursor molecule. This hypothesis will be investigated using pulse-chase experiments in vitro. A region of the gastropod brain which is rich in TRH-containing neurons will be incubated with 3H-proline. The distribution of labeled proteins and the appearances of labeled TRH will be studied after various chase times. The protein distribution will be assessed after polyacrylamide gel electrophoresis and fluorography. Labeled TRH will be quantitated after purification by HPLC and derivatization with dinitrophenol. The mechanism of TRH release will be studied in vitro in long term preoptico-posterior pituitary explants from rana catesbeiana tadpoles. The role of mono- and divalent cations and of putative neurotransmitters in the release process will be assessed. TRH will be quantitated by radioimmunoassay after acid extraction, delipidation and liquid chromatography. The possible role of TRH in osmoregulation of poikilotherms will be studied. The effect of TRH and TRH-analogues on salt transport by gastropods in vivo and on unidirectional ion flux in frog skin in vitro and on the morphology of gastropod epithelia will be assessed. Possible changes in TRH content in peripheral organs of animals which are forced to adapt to changes in temperatures and salinity of the external environment by altering salt and water transport will be studied.